Question

A server running SQL Server 2005 was converted into a virtual machine. The original server had 16 logical cores. The new virtual server only has 4 cores, but is supposed to be faster.

Some stored procedures (that may call views or UDFs) are taking longer to run. This could be due to less parallelism. But, could the query plans still be optimized for 16 cores or do they automatically re-optimize after a hardware change?

If I need to force all plans to be recalculated, what is the best way? Other thoughts?

Answer 1

Parallel Query Processing shows that the saved query plans allow for parallel processing, but are not specifically tied a particular number of threads.

There may be other reasons to periodically compile new query plans, e.g. after updating statistics. A stored procedure can be scheduled to mark all stored procedures for recompilation. I’ve had some success with the following:

create procedure [dbo].[INUpdateStatistics]
as
  set nocount on

  create table #Tables ( Table_Qualifier sysname, Table_Owner sysname, Table_Name sysname, Table_Type VarChar(32), Remarks VarChar(254) )

  declare CTable cursor local for select Table_Name, Table_Owner, Table_Type from #Tables order by Table_Name
  declare @TableName as sysname
  declare @TableOwner as sysname
  declare @TableType as sysname

  -- Get the list of tables in the database.
  insert into #Tables exec sp_tables
  open CTable
  fetch next from CTable into @TableName, @TableOwner, @TableType
  -- For each table ... .
  while @@Fetch_Status = 0
    begin
    if @TableOwner = 'dbo' and @TableType = 'TABLE'
      begin
      -- Update statistics for all user tables.
      execute( 'update statistics [' + @TableName + '] with fullscan, all' )
      -- Recompile all stored procedures and triggers when they are next executed.
      exec sp_recompile @objname = @TableName
      -- Throttle the loop.
      waitfor delay '00:00:01'
      end
    fetch next from CTable into @TableName, @TableOwner, @TableType
    end

  -- Houseclean.
  close CTable
  deallocate CTable
  drop table #Tables